Water-absorbing resin and manufacturing method

ABSTRACT

A water-absorbing resin having superior water absorption properties, and a method for manufacturing the water-absorbing resin having superior water absorption properties in a short time, in which used waste materials are used for effective utilization of resources. To this end, a high-molecular material containing acrylonitrile, styrene and conjugated dienes as constituent units are processed with acid and/or alkali.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a water absorbing resin obtained onmodifying a high-molecular material, and a manufacturing methodtherefor.

[0003] 2. Description of the Related Art

[0004] Among acrylonitrile-containing resins, there are apolystyrene-based resin, exemplified by an acrylonitrile- butadiene-styrene (ABS) resin, a styrene- acrylonitrile (SAN) resin, and anacrylonitrile- acryl- styrene (AAS) resin, and a synthetic rubber ofacrylonitrile- butadiene (NBR) rubber. These resins are relativelyinexpensive and, in particular, the former resin, that is polystyreneresin, is superior in toughness, dimensional stability and workability,and hence is used as a resin material for casing of an electricappliances or materials for various parts. The latter resin, that is thesynthetic rubber, is used as a tube, hose or a variety ofshock-absorbing material.

[0005] In these circumstances, the high-molecular materials are findinga wider field of use and expectations are made for researches towards aproduct with a higher added value. The products formed of thesehigh-molecular materials yield a large quantity of waste materials withincrease in outputs. Recently, waste materials from the high-molecularmaterials tend to be increased in quantity such that it is nowadays adesideratum to make effective use of the waste materials in keeping withrise in general interest in maintenance of global environment.

[0006] The water-absorbing resin is being used in a wide field of use,such as hygienic material, horticultural usage, food servicing, civilengineering, cosmetics and toiletry application, medical application,electronic or paint/adhesives, and is treated as necessaries of life.

[0007] The researches into use of the water-absorbing resin forafforestation of deserts are also proceeding briskly.

[0008] With increased usage of the high-molecular materials, a demandfor the properties required of them is also becoming stringent. That is,simply high water-absorbing properties are not sufficient. In the fieldof sanitary products, increase in so-called dry-touch and reduction in aleakage ratio are required, while high gelation factor is preferred towater-absorbing factor.

[0009] Thus, water-absorbing resins are being developed positively.

[0010] Meanwhile, the water-absorbing resin is mainly used forsanitation products, such as paper diaper or physiological articles. Inaddition, the water-absorbing resin is expected to be used inconstruction, horticulture, fire extinguisher or sealants, andinvestigations are going on briskly in these fields.

[0011] Under these circumstances, hydrolyzates of polyacrylonitrile oracrylonitrile/styrene copolymers are proposed. However, for thesehydrolyzates to be used as water-absorbing resin, nitrile groupcontaining polymers need to be produced. There are also raised problemssuch as time consuming reaction or insufficient water-absorbingproperties of the water-absorbing resin.

[0012] Since the water-absorbing resin for horticulture or civilengineering is used outdoors, the water-absorbing resin is required toaccommodate hostile conditions, such changes in lighting or temperature.

[0013] Also, in keeping up with general interest in upkeep of globalenvironment, needs for water-absorbing resin that can be used for desertafforestation are increasing, so that it has become necessary to furnishthese water-absorbing resins at reduced cost and in large quantities.

[0014] The waste materials, mainly composed of the high-molecularmaterials are disposed of in three different methods, that is byland-filling, incineration and re-melting. Of these, land-filling andincineration account for approximately 90%, that is, the waste materialsare hardly put to recycling.

[0015] For recycling, the waste materials are usually heat-melted andre-molded, although the waste materials that can be disposed by thismethod are limited to thermoplastic resins. There are, however, a numberof problems presented due to thermal deterioration, such as lowering inmolecular weight or oxidation of resins, mixing of foreign mater, suchas dust and dirt, or mixing of coloring agents, inorganic pigments, asreinforcements, or resins containing powdered metal pigments, thusnecessitating color matching. In this manner, recycling of the wastematerials by melting on heating has met significant impediments inconnection with the processing technique and cost.

SUMMARY OF THE INVENTION

[0016] It is therefore an object of the present invention to provide awater-absorbing resin superior in water-absorbing properties in a shorttime, and a manufacturing method thereof.

[0017] It is another object of the present invention to provide awater-absorbing resin that is able to utilize the waste materialseffectively, and a manufacturing method thereof.

[0018] It is another object of the present invention to provide awater-absorbing resin superior in stability outdoors with lapse of time,and a manufacturing method thereof.

[0019] The present invention has been fulfilled on the basis of theabove information.

[0020] In one aspect, the present invention provides a water-absorbingresin obtained on introducing an ionic group into a high-molecularmaterial containing acrylonitrile, styrene and a conjugated diene asconstituent units.

[0021] The conjugated dienes form a rubber phase in the high-molecularmaterial and is susceptible to chemical modification. Thus, it is theconjugated dienes that undergo the reaction first of all in processingwith an acid and/or an alkali. That is, with the progress in thereaction, the rubber phase of the high-molecular material containing theconjugated dienes is swollen to produce cracks in the surface of thematerial. The result is that the high-molecular material containing theconjugated dienes becomes porous in its surface due to erosion with theacid and/or alkali to increase the surface area participating in thereaction.

[0022] Thus, the reaction of the high-molecular material containing theconjugated dienes is completed in a shorter time due to the increasedsurface area participating in the reaction. Moreover, the material hassuperior water-absorbing properties due to increased surface area.

[0023] Meanwhile, in order for the conjugated dienes to be moresusceptible to reactions, the rubber phase needs to be formed in thehigh-molecular material. Therefore, the conjugated dienes are desirablycontained in the block-copolymerized state in the material.

[0024] On processing with acid and/or alkali, hydrophilic amid groups,carboxylic groups or acids thereof are introduced into the acrylonitrilepart of the high-molecular material, thus improving the water-absorbingproperties of the produced water-absorbing resin.

[0025] On acid processing in particular, strong acid groups, such assulfonic acid groups, are introduced into the styrene part of thehigh-molecular material, thus improving the water-absorbing effect ofthe produced water-absorbing resin.

[0026] By the above reason, it is desirable that 10 to 50 mol %,preferably 25 to 40 mol %, of acrylonitrile, 30 to 70%, preferably 40 to60 mol %, of styrene, 5 to 50 mol %, preferably 10 to 30 mol %, ofconjugated dienes, be contained as constituent units in thehigh-molecular material.

[0027] In the water-absorbing resin of the first aspect of the presentinvention, the high-molecular material, as the main starting material,forms a two-phase structure of a rubber phase mainly composed ofconjugated dienes and a vitreous phase composed of the styrene part andthe acrylonitrile part. Thus, if the resin is processed with an acidand/or an alkali, the vitreous phase is first reacted so that thesurface of the material becomes porous to increase the reaction surfaceto permit the reaction to proceed deep into the vitreous phase of thestyrene part or the acrylonitrile part.

[0028] By the above reason, in the water-absorbing resin of the firstaspect of the present invention, the conjugated dienes operateeffectively so that the water-absorbing resin superior inwater-absorbing properties can be produced in a shorter time thanconventionally.

[0029] If the above three constituent units are contained in theabove-mentioned pre-set amounts, it is possible for other constituentunits to be contained in the material.

[0030] These other constituent units include maleic anhydride, itaconicanhydride, α-methylstyrene, (meth)acrylamide, (meth)acrylic acid,(meth)acrylic acid ester (C1 to C10 saturated and unsaturatedhydrocarbons), vinyl acetate, vinyl chloride, ethylene, propylene,butylene, vinyl pyrrolidone and vinyl pyridine.

[0031] The weight average molecular weight (Mw) of theacrylonitrile-containing waste materials is usually 1000 to 20000000 or10000 to 1000000. If the molecular weight is less than 1000, watersolubility is demonstrated on modification, such that desirablewater-absorbing resins cannot be produced. If the molecular weightexceeds 20000000, difficulties are met in modification. However, if thehigh-molecular material is a waste material, the resin is liable toundergo cross-linking. Therefore, in this case, no limitations areimposed on the molecular weight.

[0032] Specifically, acrylonitrile- butadiene- styrene (ABS) resins arepreferred as the high-molecular material.

[0033] The high-molecular material may be a newly-produced virginmaterial, or used-up waste material, molded previously for certainpredetermined usage, such as half-products from the production processof the starting resin material or molded articles, materials for variouscomponents, such as casings used for electric appliances or cars, orbuffer materials, such as tubes or hoses. The site of putting thematerial to disposal may be a factory, a retail store or the productionprocess. The waste materials from the factory or retail stores arepreferred to those from households because the former materials aregenerally of uniform composition.

[0034] The high-molecular material may also be alloys with other resinsor contain additives, such as pigments, dyes, stabilizers, combustionretardants, plasticizers, fillers or other assistant agents. These otherresins may be enumerated by styrene-acrylonitrile (SAN) resins,acrylonitrile- styrene- acrylate (ASA) resins, acrylonitrile-chlorinatedpolystyrene- styrene (ACS) resins, acrylonitrile- nitrile- styrene (AAS)resins, acrylonitrile- butadiene rubber (NBR), polystyrene,polyphenylene ether, polycarbonate, polyphenylene sulfide, polyethyleneterephthalate, polybutylene terephthalate, polyamide (nylon) andpolyester. Of these, the SAN resin, ASA resin, AAS resin, NBR,polystyrene, polycarbonate and polyamide (nylon) are preferred.

[0035] These other different resins are preferably mixed in an amount of60 wt % or less based on the entire high-molecular material. If theother resins are contained in an amount exceeding 60 wt %, the reactionof introducing ionic groups into the waste materials tends to beimpaired.

[0036] In the second aspect, the present invention provides a method formanufacturing a water-absorbing resin including processing ahigh-molecular material having acrylonitrile, styrene and a conjugateddiene as constituent elements with an acid and/or alkali.

[0037] In the processing with alkali and/or acid, acrylonitrile in thehigh-molecular material is converted into amid or carboxylic groups orsalts thereof. On the other hand, acidic ion groups are introduced intothe styrene part, while hydroxy groups, or salts thereof and acidic iongroups, such as sulfonic acid groups, are introduced.

[0038] As the alkalis used for alkali processing, inorganic alkalis aredesirable. These inorganic alkalis are enumerated by oxides, hydroxides,carbonates, hydrogen carbonates, acetates, sulfates or phosphates ofalkali metals (sodium, lithium or potassium etc) or alkaline earthmetals (magnesium or calcium etc).

[0039] By reacting the alkalis and the high-molecular material together,the acrylonitrile part and the conjugated diene part undergo hydrolysis,whereby amide or hydroxyl groups are introduced. By adding the alkalis,the carboxylic groups or salts thereof are substituted for amid groups,while hydroxyl salts are substituted for the hydroxyl groups.

[0040] As the acids used in acidic processing, inorganic acids arepreferred. These inorganic acids may be enumerated by concentratedsulfuric acid, sulfuric anhydride, fuming sulfuric acid, sulfonatingagents, such as chlorosulfonic acid, nitric acid, fuming nitric acid,phosphorus chloride and phosphorus oxide. Of these, the sulfuric acid,sulfuric anhydride, fuming sulfuric acid and chlorosulfonic acid, inparticular concentrated sulfuric acid of the concentration of not lessthan 70 wt %, are preferred.

[0041] By reacting the inorganic acid with the high-molecular material,the acrylonitrile part is hydrolyzed and thereby modified to amide orcarboxylic groups. On the other hand, acidic ion groups, such assulfonic acid groups, —PO(OH)2, —CH2PO(OH)2 or nitro groups, areintroduced into the styrene part or the conjugated diene part.

[0042] If sulfonating agents are used in the above-mentioned acidprocessing, Louis bases may be concomitantly used. These Louis bases maybe enumerated by alkyl phosphates (triethyl phosphate, trimethylphosphate or trimethyl phosphate), dioxane, acetic anhydride, ethylacetate, ethyl palmitate, diethyl ether and thioxane. In the presentacidic processing, the amount of addition of the Louis bases is 1 to 200mol %, preferably 2 to 100 mol %, to the entire monomer unit in thehigh-molecular material. If, in the present acidic processing, theamount of addition of the Louis bases may be enumerated by alkylphosphate (triethyl phosphate and trimethyl phosphate), dioxane, aceticanhydride, ethyl acetate, ethyl palmitate, diethyl ether and thioxane.In the present acidic processing, the amount of the Louis bases, used inconjunction, is 1 to 200 mol % and preferably 2 to 100 mol % based onthe entire monomer unit in the high-molecular material. If the amount ofaddition of the Louis bases is less than the above-mentioned range,gelated products undesirably tend to be produced in the reaction. If theamount of the Louis bases exceeds the above-mentioned range, thesulfonating reaction undesirably cannot proceed without difficulties.

[0043] The charging quantity of the alkali and/or acid, which isaffected significantly by the concentration of the alkali or acid, isusually 1 to 500 and preferably 5 to 200 times the weight of thehigh-molecular material.

[0044] If the charging quantity of the alkali and/or acid is too small,the rate of introduction of the ion groups to styrene or conjugateddienes as well as the rate of acrylonitrile hydrolysis is lowered todeteriorate the performance (water-absorbing properties) as thewater-absorbing resin. Conversely, if the charging quantity of thealkali and/or acid is excessive, it becomes necessary to wash the excessalkali and/or acid with water for neutralization, which is notmeritorious economically or for operation.

[0045] The alkali and/or acid may be used alone or in combination. Inthe latter case, the alkali and/or acid may be mixed or addedsequentially. However, the alkali and the acid are not mixed in use. Theprocessing with alkali may be carried out following acidic processing orvice versa. Alternatively, processing with concentrated sulfuric acidmay be followed by processing with sulfuric anhydride (acidic processingis followed by acidic processing).

[0046] The processing with alkali and/or acid may be performed in thefollowing manner.

[0047] (1) Preferably, the concentrated sulfuric acid or chlorosulfonicacid is first added to the high-molecular material followed by additionof one of the sulfuric anhydride or fuming sulfuric acid. By thistechnique, sulfonic acid groups are introduced into styrene orconjugated diene part in the high-molecular material as a result ofaddition of one of the concentrated sulfuric acid or the chlorosulfonicacid. If one of the sulfuric anhydride or fuming sulfuric acid is added,the high-molecular material is cross-linked. Thus, with the presenttechnique, a water-absorbing resin having high cross-linking degree canbe produced and hence a highly functional aqueous type resin having highshape stability can be produced.

[0048] (2) The sulfonic acid groups can be introduced into thehigh-molecular material by first reacting the sulfonating reaction(sulfuric anhydride, fuming sulfuric acid, chlorosulfonic acid,concentrated sulfuric acid etc) with the high-molecular material in asolvent. Alternatively, carboxylic groups can be introduced into thehigh-molecular material by adding n-butyl lithium to the solvent andreacting the resulting product with dry ice. Still alternatively,—PO(OH)2 groups can be introduced into the high-molecular material byadding phosphorus trichloride and subjecting the resulting product tohydrolysis.

[0049] (3) The waste materials of polystyrene-based waste resin materialmay be chlorometylated with chloromethyl ether and the Louis acids andreacted with ammonia or a variety of amine compounds to introducetertiary or quaternary amine salts as ion groups into the resin.Alternatively, the polystyrene based waste resin material may be reactedwith the chlorometylated product and phosphorus trichloride and thereaction product is hydrolyzed to introduce —PO(OH)2 group into thepolystyrene based waste resin material.

[0050] (4) By reaction with a liquid mixture of sulfuric acid and nitricacid, —NO2 groups can be introduced into the polymer.

[0051] The above-described modification processing may be carried out inalkali or acid or in a system employing an organic solvent.

[0052] The solvents used in the reaction system may be enumerated by C1to control switch 2 aliphatic halogenated hydrocarbons, preferably 1,2-dichloroethane, chloroform, dichloromethane or 1,1-dichloroethane,aliphatic cyclic hydrocarbons, preferably cyclohexane, methylcyclohexane or cyclopentane, nitromethane, sulfur dioxide, C1 to C7paraffinic hydrocarbons, acetonitrile, carbon disulfide,tetrahydrofuran, tetrahydropyran, 1,2- dimethoxy ethane, acetone,methylethylketone, and thiophen. Of these, C1 to C2 aliphatichalogenated hydrocarbons, aliphatic cyclic hydrocarbons, nitromethanenitrobenzene and sulfur dioxide are preferred. These solvents may beused alone or in combination. There is no particular limitation to themixing ratio for the above solvents.

[0053] The amount of addition of the organic solvents is preferably lessthan approximately 200 times the weight of the high-molecular material.If the amount of addition of the organic solvent exceeds this range, themodification processing is non-desirably lowered in reaction ratio.

[0054] The alkali, acid or the organic solvent, once used in themodification, may be recovered after the end of the reaction anddirectly re-used for reaction.

[0055] Meanwhile, it is desirable that the high-molecular material asthe starting material in the above-described processing with alkaliand/or acid be comminuted in particle size. By increasing the surfacearea of the high-molecular material, the modified portion may beincreased to improve the rate of introduction on the ion groups into thehigh-molecular material.

[0056] For comminuting the particle size of the high-molecular material,such as polystyrene based resins, blocks of the high-molecular materialmay be mechanically pulverized and sieved. If the waste materials areused as the high-molecular material, it is desirable to freeze the wastematerials at lower temperature followed by pulverization, because rubbercomponents may be contained in the material.

[0057] For comminuting the particle size of the high-molecular material,such as polystyrene based resin, the high-molecular material ispreferably of such a piece size as to pass through the mesh not smallerthan 3.5 mesh. If the piece size of the high-molecular material islarger than this value, the surface of the reacted product becomes toosmall to render modification difficult to protract the reactionundesirably. Moreover, the properties of the water-absorbing resin(water-absorbency) are significantly lowered.

[0058] In the reaction of introducing the ion groups into theabove-mentioned high-molecular material, dispersants may be added to thereaction system when introducing ion groups. This disperses thehigh-molecular material satisfactorily in the reaction system, thusimproving the ionic group introducing rate.

[0059] The reaction temperature for the above-described modification is0 to 200°C. and preferably 30 to 150° C., although it may varysignificantly depending on the type of the alkali or acid or on whetheran organic solvent is used. If the temperature is too low, the reactionundesirably tends to be retarded. Also, the ion group introducing ratetends to be lowered to render it impossible to realize the goodwater-absorbing effect. If, conversely, the temperature is too high, themolecular chain of the high-molecular material tends to be disrupted bythermal decomposition, with the resin exhibiting water-solubility andbecoming unusable as water-absorbing resin.

[0060] The reaction time, which varies significantly with the reactiontemperature, is usually 1 minute to 40 hours and preferably 5 minutes to10 hours. If the reaction is too short or too long, the reaction cannotproceed sufficiently or the production efficiency is worsened.

[0061] The reaction product, into which are introduced ion groups by theprocessing with alkali or acid, is preferably washed in its entiretywith a large quantity of water or neutralized with an aqueous solutionof opposite properties. Alternatively, the reaction mass may be filteredfrom the reaction system and injected into a large quantity of water oran aqueous solution of opposite properties for washing. On washing, partof acrylonitrile groups are hydrolyzed such that the reaction product istuned into acrylamide and improved in hydrophilicity.

[0062] The resulting modified product is gelated and hence is driedunder the sun, on heating, pressure reduction, centrifugation or pressworking to provide a desired water-absorbing resin.

[0063] By the above-described processing of the second aspect of thepresent invention, nitrile groups of the acrylonitrile part in thehigh-molecular material are hydrolyzed into amide groups, carboxylicgroups and/or salts thereof. Into the double bonds of the conjugateddienes in the high-molecular material are introduced, on hydrolysis,hydroxyl groups and/or salts thereof or acidic ionic groups. Into thebenzene ring of the styrene part are introduced acidic ion groups.

[0064] The amide groups, carboxyl groups and/or salts thereof, hydroxylgroups and/or salts thereof, are required for improving the absorptionfor water, such that benzene groups or acidic ion groups introduced intothe double bond improve the water absorption properties with respect tothe aqueous electrolyte solution. Meanwhile, the cross-linked portioninherently present in the ABS resin is not water-soluble following theabove reaction to contribute to formation of the water-absorbing resinhaving strong gel strength.

[0065] The water-absorbing resin thus produced may be used for a varietyof usages, such as sanitary articles, including paper diaper orphysiological products, materials for construction, agriculture orhorticulture, aimed to accord water retention properties to the soil, orfor desert afforestation, aroma retention agents for assuring durabilityof the aromatic agent, dehydrators from organic/inorganic materials,pharmaceuticals for digestion, sealing agents, packing agents,anti-dewing agents, coating agents, desiccants, water processing agentsetc.

[0066] In the third aspect, the present invention provides awater-absorbing resin wherein an ionic group is introduced into ahigh-molecular material containing inorganic pigments and/or metalpowders and acrylonitrile.

[0067] In the high-molecular material containing inorganic and/ororganic pigments, the reaction of modification is accelerated since thepigments tend to be disengaged from the surface of the material torender the surface porous to increase the reaction surface. This poroussurface is then softened by the activated reaction of modification.Thus, the pigment lying at a deeper site is desorbed from the materialto accelerate the reaction of modification.

[0068] By the above reason, the reaction of modification of thehigh-molecular material containing the pigment is accelerated so thatthe surface of the as-modified high-molecular material is porous to adeep site. Therefore, the water-absorbing resin produced from thishigh-molecular material is increased in water-absorbing surface andthereby drastically improved in water-absorbing factor andwater-absorbing speed.

[0069] The content of the inorganic pigment and/or the powdered metalmaterial is 0.01 to 20 wt % and preferably 0.06 to 10 wt %.

[0070] If the content of the pigments is small, the modificationreaction accelerating effect proper to the high-molecular material islowered. If conversely the pigment content is excessive, economicdemerits are raised, or the modification reaction becomes difficult tocontrol.

[0071] The inorganic pigment and the powdered metal material preferablyexhibits good dispersion properties with respect to the above-mentionedhigh-molecular material. Examples of the inorganic pigment and thepowdered metal material include carbon black, iron black, titaniumoxide, zinc flower, iron oxide red, ultramarine, berlin blue, cobaltblue, lithopone, zinc sulfide, antimony oxide, yellow iron oxide, amber,sienna, ochre, pyridian, aluminum powders and bronze powders. Of these,carbon black and titanium oxide are preferred.

[0072] It is noted that carbon black used may be manufactured by any ofa channel method, a furnace method and thermal melting method. Thesemethods may be used alone or in combination. The mean particle size is 5to 500 μm and preferably 1- to 50 μm.

[0073] Titanium oxide may be of the rutile-, anatase- or long fineparticulate titanium type. These different types may be used aline or incombination. The mean particle size is 0.01 to 50 μm and preferably 0.05to 10 μm.

[0074] These inorganic pigments or the powdered metal materials may becontained alone or as a mixture in the high-molecular material.

[0075] These inorganic pigments or the powdered metal materials may beadded to the high-molecular material for preparing the water-absorbingresin and/or as coloring, covering or reinforcing agents or as agentsfor according electrically conductivity.

[0076] In the fourth aspect, the present invention provides a method formanufacturing a water-absorbing resin including processing ahigh-molecular material containing an inorganic pigment and/or metalpowder pigments and acrylonitrile with an alkali and/or an acid tointroduce an ionic group.

[0077] The ion groups may be added to a high-molecular materialcontaining the inorganic pigments and/or the powdered metal pigments andacrylonitrile by the alkali processing and/or acid processing asdescribed above.

[0078] In the fifth aspect, the present invention provides awater-absorbing resin mainly containing a high-molecular material havingan ionic group introduced therein and also containing a stabilizer.

[0079] It is noted that the high-molecular material, having introducedtherein the ion groups as the major portion of the water-absorbing resinof the fifth aspect of the present invention, may be enumerated by

[0080] (1) acrylic acid, salts thereof, and cross-linked polymersthereof produced by, for example: sodium acrylate+cross-linking agents(cross-linking monomers) polymerization→drying;

[0081] (2) polymers obtained on graft polymerization of starch orpolyvinyl alcohol to acrylic acid, salts thereof or acrylonitrile, suchas those obtained by

[0082] a. starch+acrylic acid cross-linking agents→graftpolymerization→hydrolysis→drying;

[0083] b. starch+acrylonitrile→graftpolymerization→hydrolysis→neutralization drying;

[0084] (3) hydrolyzates of acrylic fibers, such as those obtained by thefollowing method: acrylonitrile+acrylic acid+N-methylolacrylamide→polymerization→spinning→hydrolysis→drying;

[0085] (4) crosslinked polymers of polyvinyl alcohol, such as thoseobtained by: polyvinyl alcohol→cross-linking (o-phosphoric acid,radiations etc)→drying;

[0086] (5) hydrolyzates (acid processed product) of a polymer containingacrylonitrile and, if necessary, styrene or conjugated dienes.

[0087] Among a number of stabilizers, there are those havinganti-oxidation effect, such as, phenolic, sulfur-based, phosphorus-basedstabilizers, erysorbic acid, sodium erysorbate, and isopropyl citrate.

[0088] There are also those having light stabilizing effect, such asbenzophenone based, benzotriazole-, hindered amine,cyano-acrylate-based, salicylate-based, or oxalic acid anilide basestabilizers.

[0089] These stabilizers may be contained alone or as a mixture in thewater-absorbing resin. It is noted that plural different stabilizersrather than the same stabilizers, such as anti-oxidants or lightstabilizers, are preferably contained in the water-absorbing resin forassuring stabilizing effects against different factors, such as light orheat.

[0090] These stabilizers may be directly added to the high-molecularmaterial containing the above ion groups or previously added to thestarting polymer if ion groups are to be introduced. Alternatively, thestabilizers may be added to the water-absorbing resin during manufacturethereof, or added in plural stages described above.

[0091] For adding the stabilizers directly to the water-absorbing resin,the stabilizers may be blended individually to the water-absorbingresin, or an aqueous solution in which the stabilizers are dispersed ordissolved in advance may be absorbed to the water-absorbing resin.

[0092] For adding the stabilizers at the time of manufacture to awater-absorbing resin obtained on graft polymerization of acrylic acidto starch, the stabilizers may be added to the reaction system followingthe graft polymerization and neutralization, and the resulting mass maythen be dried. If the water-absorbing resin is of the cross-linkedsodium acrylate, the stabilizers may be added and dried followingpolymerization by sodium acrylate and the cross-linking agent. Since thestabilizers tend to capture radicals and hence the stabilizers addedprior to polymerization tend to obstruct the polymerization, thestabilizers are preferably added following the polymerization.

[0093] The stabilizers are previously added to the starting polymer inthe case of the waste ABS resins (if the amount of addition of thestabilizer is insufficient, the deficit stabilizers are to be addednewly). These resins are processed with heated sulfuric acid, washedwith water and dried to complete the water-absorbing resin.

[0094] If the stabilizer is contained in the stating polymer, thehigh-molecular material containing the stabilizer is hydrolyzed tointroduce the ion groups.

[0095] Irrespective of the manufacturing methods used, the amount ofaddition of the stabilizers is preferably 0.00001 to 20 wt % and morepreferably 0.0001 to 5 wt % based on the dry weight of thewater-absorbing resin. If the amount of addition is smaller than this,the effect of the stabilizer is impaired. If the amount of addition islarger than this, the properties of the water-absorbing resin may beimpaired while the cost is undesirably raised.

[0096] By adding the stabilizer to the water-absorbing resin product orduring manufacture thereof, heating oxidation or photo-oxidationreaction is suppressed to prevent the molecular weight of thewater-absorbing resin from being lowered. The result is thewater-absorbing resin superior in chronological stability for outdooruse.

[0097] In the sixth aspect, the present invention provides a method formanufacturing a water-absorbing resin including introducing a stabilizerinto a high-molecular material into which is previously introduced anionic group, or hydrolyzing a stabilizer-containing high-molecularmaterial to introduce an ionic group.

[0098] The ion groups can be introduced into the high-molecular materialby the acid processing and/or alkali processing such as those describedabove.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0099] The first and second embodiments of the present invention will beexplained in detail.

EXAMPLE 1

[0100] An ABS resin, containing, as constituent units, 44 mol % ofstyrene units, 29 mol % of acrylonitrile units and 28 mol % of butadieneunit, with 1 wt % of titanium oxide as an inorganic pigment, wasfreeze-pulverized to a pulverized product with 32 to 150 mesh size. 3 gof the pulverized product were added to 90 g of 96 wt % sulfuric acidand reacted at 80° C. for five minutes. After the end of the reaction, asolidified product in the reaction system was filtered through a glassfilter, washed with water and dried by a circulating type drier at 115°C. for two hours to give a water-absorbing resin (Example 1).

[0101] The sulfonic acid groups in the water-absorbing resin (Example 1)accounted for 35 mol % of the entire monomer unit.

EXAMPLE 2

[0102] A used guard panel of the 8 mm cassette tape (black-coloredportion), formed of a waste ABS resin containing, as constituent units,50 mol % of styrene units, 35 mol % of acrylonitrile units, 15 mol % ofbutadiene unit and 1 wt % of carbon black, was pulverized to a size of32 to 50 mesh.

[0103] 3 g of the pulverized product was added to 90 g of 89 wt %concentrated sulfuric acid and reacted at 60° C. for 20 minutes. Thereaction system was then cooled to ambient temperature and added to with0.5 g of 60 wt % fuming sulfuric acid to continue the reaction forfurther ten minutes. After the end of the reaction, the solid productwas filtered by a glass filter, washed with water and dried for twohours by a direr to a water-absorbing resin (Example 2).

[0104] The sulfonic acid groups in the water-absorbing resin (Example 2)accounted for 45 mol % of the entire monomer unit.

EXAMPLE 3

[0105] The pulverized ABS resin of Example 1 was added to a 5 wt % of anaqueous solution and reacted at 95° C. for one hour. After the end ofthe reaction, the solid mass in the reaction system was filtered, washedwith water and dried for two hours in a drier to a water-absorbing resin(Example 3).

[0106] The sulfonic acid groups in the water-absorbing resin (Example 3)accounted for 25 mol % of the entire monomer unit.

EXAMPLE 45

[0107] The ABS resin of the same resin composition as Example 1, notcontaining titanium oxide (natural type), was freeze-dried to a 32 to150 mesh pulverized product, which then was processed in the same manneras in Example 1 to give a water-absorbing resin (Example 4).

[0108] The sulfonic acid groups in the water-absorbing resin (Example 4)accounted for 20 mol % of the entire monomer unit.

COMPARATIVE EXAMPLE 1

[0109] A water-absorbing resin (Comparative Example 1) was produced inthe same way as in Example 1 except using a SAN resin reagent(containing, as constituent units, 60 mol % of styrene unit and 40 mol %of acrylonitrile unit, and not containing the pigment) as a startingmaterial.

[0110] The sulfonic acid group of the water-absorbing resin (ComparativeExample 1) accounted for 12 mol % of the entire monomer unit.

COMPARATIVE EXAMPLE 2

[0111] A water-absorbing resin (Comparative Example 2) was produced inthe same way as in Example 1 except using a HIPS resin reagent(containing 60 mol % of a styrene unit and 40 mol % of a butadiene unitwithout containing pigments) as a starting material to give awater-absorbing resin (Comparative Example 2).

[0112] The sulfonic acid groups in this water-absorbing resin(Comparative Example 2) accounted for 9 mol % of the entire monomerunit.

COMPARATIVE EXAMPLE 3

[0113] A water-absorbing resin (Comparative Example 3) was produced inthe same way as in Example 1 except using NBR reagent (containing 22 mol% of acrylonitrile unit and 78 mol % of butadiene unit withoutcontaining pigments) as a starting material to give a water-absorbingresin (Comparative Example 3).

[0114] The sulfonic acid groups in this water-absorbing resin(Comparative Example 3) accounted for 14 mol % of the entire monomerunit.

COMPARATIVE EXAMPLE 4

[0115] A water-absorbing resin (Comparative Example 4) was produced inthe same way as in Example 2 except using the SAN resin of ComparativeExample 1 to give a water-absorbing resin (Comparative Example 4).

[0116] The sulfonic acid groups in this water-absorbing resin(Comparative Example 4) accounted for 14 mol % of the entire monomerunit.

COMPARATIVE EXAMPLE 5

[0117] A water-absorbing resin (Comparative Example 5) was produced inthe same way as in Example 3 except using the SAN resin of ComparativeExample 1 to give a water-absorbing resin (Comparative Example 5).

[0118] The sodium carbonade group in the water-absorbing resin(Comparative Example 5) accounted for 10% of the entire monomer unit.

[0119] Evaluation of Properties 1

[0120] The water absorption properties of the water-absorbing resins ofthe Examples 1 to 4 and the Comparative Examples 1 to 5 were checked inthe following manner.

[0121] Each 1 g of the water-absorbing resins of the Examples andComparative Examples was dipped in pure water to check the weight afterlapse of one minute, two minutes and four minutes. The results are shownin Table 1. TABLE 1 weight (g) after lapse of 1 after lapse of 2 afterlapse of 4 minute minutes minutes Ex. 1 98 97 101 Ex. 2 109 110 111 Ex.3 90 95 93 Ex. 4 51 65 66 Comp. Ex. 1 39 50 51 Comp. Ex. 2 1.1 1.1 1.1Comp. Ex. 3 2.1 3.1 3.1 Comp. Ex. 4 32 47 48 Comp. Ex. 5 23 34 34

[0122] From the results of table 1, the water-absorbing resinscontaining all three units of styrene, acrylonitrile and conjugateddiene (Examples 1 to 4) are superior in both the water-absorbing rateand in water-absorbing factor as compared to the water-absorbing resinsnot containing all these three units (Comparative Examples 1 to 5).

[0123] As may be seen on comparing the results of Examples and 4, thewater-absorbing rate and the water-absorbing factor may be furtherimproved by further containing an inorganic pigment.

[0124] Up to now, the waste ABS resin materials can hardly be re-usedbecause the resin composition is varied from one product to another andthe properties are drastically lowered on re-melting. According to thepresent invention, the waste ABS resin can be used as a startingmaterial to render it possible to make more effective utilization ofresources.

[0125] Evaluation of Properties 2

[0126] The water absorption properties of the water-absorbing resins ofthe Examples 1 to 4 and the Comparative Examples 1 to 5 wee checked inthe following manner.

[0127] Each 1 g of the water-absorbing resins of the Examples andComparative Examples was dipped in 1 wt % of calcium chloride to checkthe weight after lapse of one minute, two minutes and four minutes. Theresults are shown in Table 2. TABLE 2 weight (g) after lapse of oneafter lapse of two after lapse of three minute minutes minutes Ex. 1 4647 47 Ex. 2 53 55 55 Ex. 3 32 38 38 Ex. 4 18 2 22 Comp. Ex. 1 12 17 18Comp. Ex. 4 15 20 21 Comp. Ex. 5 3 5 5

[0128] From the results of table 2, the water-absorbing resinscontaining all three units of styrene, acrylonitrile and conjugateddiene (Examples 1 to 4) are superior in water absorption properties withrespect to the artificial urine and an aqueous electrolytic solution(aqueous solution of divalent metal salts)as compared to thewater-absorbing resins containing none of these three units (ComparativeExamples 1, 4 and 5).

[0129] As may be seen on comparing the results of Examples 1 and 4, thewater-absorbing rate and the water-absorbing factor may be furtherimproved by further containing an inorganic pigment.

[0130] The third and fourth embodiments of the present invention arehereinafter explained with reference to further illustrativeembodiments.

EXAMPLE 5

[0131] An ABS resin containing, as constituent units, 52 mol % of astyrene unit, 29 mol % of an acrylonitrile unit and 19 mol % of abutadiene unit, and also containing 1 wt % of carbon black, wasfreeze-pulverized to a mesh size of 16 to 65 mesh. 3 g of thispulverized product was added to 90 g of 89 wt % concentrated sulfuricacid and reacted at 80° C. for 20 minutes. After the end of thereaction, the solid substance in the reaction system was filteredthrough a glass filter, washed with water and dried in a circulatingtype drier at 115° C. for two hours to give a black coloredwater-absorbing resin (Example 5).

[0132] The sulfonic acid groups in this water-absorbing resin(Example 1) accounted for 42 mol % of the entire monomer unit.

EXAMPLE 6

[0133] A used guard panel of the 8 mm cassette tape (transparentportion), formed of a waste SAN resin containing, as constituent units,64 mol % of styrene units and 36 mol % of acrylonitrile units, withoutcontaining inorganic pigments, was pulverized to particle size of 16 to65 mesh. To this pulverized product were added 2 wt % of titanium oxidepowers and kneaded using a small-sized extruder at 250°.

[0134] 3 g of the pulverized product was added to 90 g of 96 wt %concentrated sulfuric acid and reacted at 60° C. for 60 minutes. Thereaction product was allowed to cool to room temperature and added towith 0.5 g of 60 wt % fuming sulfuric acid. The reaction was continuedfurther for 30 minutes. After the end of the reaction, the solid mass inthe reaction system was filtered through a glass filter, washed withwater and dried by a drier for two hours. A pale yellow water-absorbingresin (Example 6) was obtained.

[0135] The sulfonic acid groups in this water-absorbing resin (Example6) accounted for 51 mol % of the entire monomeric unit.

EXAMPLE 7

[0136] The procedure of Example 1 was followed except using a casing ofa used personal computer (waste ABS material containing, as constitutingunits, 46 mol % of a styrene unit, 36 mol % of acrylonitrile unit and 19mol % of a butadiene unit, and also containing 1 wt % of carbon black,as inorganic pigment). A black water-absorbing resin (Example 7) wasobtained.

[0137] The sulfonic acid groups in this water-absorbing resin (Example7) accounted for 38 mol % of the entire monomeric unit.

EXAMPLE 8

[0138] The pulverized ABS resin, which is the same starting material asthat of Example 5, was added to a 7 wt % aqueous solution of sodiumhydroxide, and reaction was carried out at 98° C. for two hours. Afterthe end of the reaction, the solid mass in the reaction system wasfiltered, washed with water and filtered for two hours in a drier. Ablack water-absorbing resin (Example 8) was produced.

[0139] The sodium carboxylate in the water-absorbing resin (Example 8)accounted for 34 mol % of the entire monomer unit.

COMPARATIVE EXAMPLE 6

[0140] An ABS resin (natural type) having the same resin composition asthat of Example 6 and not containing pigments (carbon black) wasfreeze-dried to the size of 16 to 65 mesh. This pulverized product wasprocessed in the same way as in Example 5 to produce a pale orangecolored water-absorbing resin (Comparative Example 6).

[0141] The sulfonic acid groups in the water-absorbing resin(Comparative Example 6) accounted for 27 mol % of the entire monomerunit.

COMPARATIVE EXAMPLE 7

[0142] The processing was carried out in the same manner as in Example2, except not adding titanium oxide, to produce a transparentwater-absorbing resin (Comparative Example 7).

[0143] The sulfonic acid groups in the water-absorbing resin(Comparative Example 7) accounted for 27 mol % of the entire monomerunit.33

COMPARATIVE EXAMPLE 8

[0144] An ABS resin (natural type) having the same resin composition asthat of Example 5 and not containing pigments (carbon black) wasfreeze-dried to the size of 16 to 65 mesh. This pulverized product wasprocessed in the same way as in Example 4 to produce a yellowwater-absorbing resin (Comparative Example 8).

[0145] The sodium carboxylate groups in the water-absorbing resin(Comparative Example 8) accounted for 22 mol % of the entire monomerunit.

[0146] Evaluation of Properties 3

[0147] The water absorption properties of the water-absorbing resins ofthe Examples 5 to 8 and the Comparative Examples 6 to 8 were checked inthe following manner.

[0148] Each 1 g of the water-absorbing resins of the Examples andComparative Examples was dipped in pure water to check the weight afterlapse of 30 seconds, two minutes and five minutes. The results are shownin Table 3. TABLE 3 wt.(g) after lapse of 30 after lapse of two afterlapse of four seconds minutes minutes Ex. 5 105 110 112 Ex. 6 84 90 81Ex. 7 98 102 102 Ex. 8 80 82 85 Comp. Ex. 6 53 68 72 Comp. Ex. 7 47 5861 Comp. Ex. 8 42 50 52

[0149] From the results of Table 3, it is seen that the water-absorbingresin containing an inorganic pigment (Examples 5 to 8) is superior inwater-absorbing rate and water-absorbing factor as compared to thewater-absorbing resin not containing inorganic pigments (ComparativeExamples 6 to 8).

[0150] It is also seen that, by the application of the manufacturingmethod of the present invention, the water-absorbing resin employing thewaste ABS resin having substantially the same composition as that ofExample 5 (the resin of Example 8) shows superior water-absorbing rateand water-absorbing factor.

[0151] Evaluation of Properties 4

[0152] Of the water-absorbing resins of the Examples 5 to 8 andComparative Examples 6 to 8, the water-absorbing properties were checkedin the following manner.

[0153] Each 1 g of the Examples and Comparative Examples was dipped inartificial urea and 1 wt % of calcium chloride to measure the weightafter lapse of five minutes. The results are shown in Table 4. TABLE 4weight (g) artificial urine calcium chloride Ex. 5 69 44 Ex. 6 53 35 Ex.7 63 40 Ex. 8 50 32 Comp. Ex. 6 44 22 Comp. Ex. 7 40 20 Comp. Ex. 8 3317

[0154] From the results of Table 4, it is seen that the water-absorbingresin containing an inorganic pigment (Examples 5 to 8) is superior inwater-absorbing properties for the artificial urine or aqueouselectrolytic solutions (aqueous solutions of divalent metal salts) ascompared to the water-absorbing resin not containing inorganic pigments(Comparative Examples 6 to 8).

[0155] It is also seen that, by the application of the manufacturingmethod of the present invention, the water-absorbing resin employing thewaste ABS resin having substantially the same composition as that ofExample 5 (the resin of Example 8) exhibit superior water absorptionproperties.

[0156] The fifth and sixth aspects of the present invention arehereinafter explained.

EXAMPLE 9

[0157] A casing of a used personal computer, formed of a waste ABSmaterial containing, as a resin composition, 48 mol % of a styrene unit,39 mol % of acrylonitrile unit and 13 mol % of a butadiene unit, andalso containing 0.2 wt % of stearyl-β-(3, 5-di-t-butyl-4- hydroxyphenyl) propionate, a stabilizer, was freeze-pulverized to a pulverizedresin material of 32 to 65 mesh size.

[0158] 3 g of this pulverized product was added to 90 g of concentratedsulfuric acid (concentration: 96 wt %) and reacted at 80° C. for 20minutes. After the end of the reaction, a solid product in the reactionsystem was filtered through a glass filter, washed with water and driedby a circulating type drier at 115° C. for two hours.

[0159] A black water-absorbing resin was obtained.

[0160] The sulfonic acid groups in the water-absorbing resin accountedfor 38 mol % of the entire monomer unit, with the content of thestabilizer being 0.012 wt % on the dry weight basis.

EXAMPLE 10

[0161] A guard panel (transparent portion) of a used 8 mm cassette tape,formed of a waste SAN resin containing, as a resin composition, 64 mol %of a styrene unit and 36 wt % of an acrylonitrile unit, and alsocontaining, as stabilizers, 0.2 wt % of tetrakis (2, 2, 6, 6-tetramethyl-4-piperidyl-1, 3, 4- butane tetracarboxylate and 0.1 wt % ofstearyl-β-(3, 5-di-butyl-4-hydroxy phenyl) propionate, was pulverized toa resin product having a mesh size of 32 to 65.

[0162]3.5 g of this pulverized product were added to 90 g ofconcentrated sulfuric acid having a concentration of 89 wt % and reactedat 60° C. for 60 minutes. 0.5 g of fuming sulfuric acid, containing 60wt % of SO3, was added to the reaction system and reacted further for 30minutes.

[0163] After the end of the reaction, the solid mass in the reactionsystem was filtered through a glass filter, washed with water and driedby a drier for two hours. A transparent water-absorbing resin wasproduced.

[0164] The sulfonic groups in the water-absorbing resin (Example 10)accounted for 47 mol % of the entire monomer unit. The content of theformer stabilizer was 0.01 wt %, while that of the latter stabilizer was0.008 wt %, on the dry weight basis.

EXAMPLE 11

[0165] Starch was α-processed and charged so that the starch to acrylicacid ratio was 20/80 wt %, with the polymerization concentration being20 wt %, and polymerization was carried out using a redox catalyst (H2O2catalyst: 0.1 mol %).

[0166] After the end of the polymerisation, 70 mol % of the polyacrylicacid fraction was neutralized with sodium hydroxide and sodiumerysorbate was kneaded into a polymer gel in an amount of 0.01 wt %based on the pure polymer content.

[0167] The resulting product was dried by a drier to produce astabilizer-containing water-absorbing resin.

EXAMPLE 12

[0168] In 1 g of a commercial cross-linked sodium polyacrylatewater-absorbing resin were absorbed 5 g of a 0.001 wt % aqueous solutionof 1,1, 3-tris(2- methyl-4-hydroxy-5-t-butylphenyl) butane andsubsequently dried to give a stabilizer-containing water-absorbingresin.

EXAMPLE 13

[0169] In 1 g of a commercial polyvinyl cross-linked water-absorbingresin were absorbed 2 g of 0.002 wt % ethanolic solution of phenylsalicylate and subsequently dried to give a stabilizer-containingwater-absorbing resin.

COMPARATIVE EXAMPLE 9

[0170] A SAN reagent resin, containing 60 mol % of styrene and 40 mol %of acrylonitrile without containing a stabilizer was pulverized andclassified to recover a solid article of 32 to 65 mesh size.

[0171] This solid mass was processed in the similar manner to Example 10to produce a transparent water-absorbing resin. The sulfonic acid groupsin the water-absorbing resin accounted for 44 mol % of the entiremonomer unit. This water-absorbing resin was termed a resin ofComparative Example 9.

COMPARATIVE EXAMPLE 10

[0172] A commercial starch/sodium acrylate graft water-absorbing resinwas termed a resin of Comparative Example 10.

COMPARATIVE EXAMPLE 11

[0173] A commercial cross-linked sodium polyacrylate water-absorbingresin was termed a resin of Comparative Example 11.

COMPARATIVE EXAMPLE 12

[0174] A commercial polyvinyl alcohol cross-linked water-absorbing resinwas termed a resin of Comparative Example 12.

[0175] Of the above water-absorbing resins of the Examples 9 to 13 andthe Comparative Examples 9 to 12, chronological stability was evaluatedby the following method:

[0176] Evaluation 5

[0177] The above water-absorbing resins and the same resins swollen to avolume 50 times the original volume were heated and dried in an oven at90° C. for 100 hours.

[0178] After this heating processing, changes in the water-absorbingfactor relative to pure water (rate of decrease of the water-absorbingefficiency)[(water-absorbing factor after heatingprocessing/water-absorbing factor before heating) X 100(%)] weremeasured and compared. The results are shown in Table 5. TABLE 5 onlywater- swollen water- samples absorbing resin absorbing resin Ex.9 >95%   >95%   Ex. 10 92% 88% Ex. 11 78% 70% Ex. 12 72% 64% Ex. 13 82%75% Comp. Ex. 9 42% 33% Comp. Ex. 10 <10%   <10%   Comp. Ex. 11 <10%  <19%   Comp. Ex. 12 18% <10%  

[0179] It is seen from this Table 5 that the inventive Examples 9 to 13show chronological stability with respect to heat superior to those ofthe Comparative Example 9 to 12.

[0180] Evaluation 6

[0181] The above water-absorbing resins and the same resins swollen to avolume 50 times the original volume were irradiated for 50 hours with a15W/100 V lamp spaced 50 cm from the resins.

[0182] The resins obtained after irradiation and those not irradiatedwere dried under the same conditions of 90°C. two hours and thedifference of the water-absorption factor of the produced resins to purewater[(irradiated products/non-irradiated products) X 100 (%)] wasmeasured and compared. The results are shown in Table 6. only water-swollen water- samples absorbing resin absorbing resin Ex. 9 94% 95% Ex.10 87% 89% Ex. 11 85% 83% Ex. 12 82% 80% Ex. 13 83% 80% Comp. Ex. 9 58%60% Comp. Ex. 10 49% 44% Comp. Ex. 11 21% 18% Comp. Ex. 12 22% 20%

[0183] It is seen from table 6 that the inventive Examples 9 to 13 aresuperior in chronological stability to light superior to the ComparativeExample 9 to 12.

What is claimed is:
 1. A water-absorbing resin obtained on introducingan ionic group into a high-molecular material containing acrylonitrile,styrene and a conjugated diene as constituent units.
 2. Thewater-absorbing resin according to claim 1 wherein the conjugated dienein said high-molecular material is in the form of a block copolymer. 3.The water-absorbing resin according to claim 1 wherein thehigh-molecular material contains, as constituent units, 10 to 50 mol %of acrylonitrile, 30 to 70 mol % of styrene and 5 to 50 mol % of theconjugated diene.
 4. The water-absorbing resin according to claim 1wherein the high-molecular material is anacrylonitrile-butadiene-styrene resin.
 5. The water-absorbing resinaccording to claim 1 wherein the high-molecular material is a wastematerial comprised of a used resin molded for specified usage.
 6. Thewater-absorbing resin according to claim 1 wherein said high-molecularmaterial contains an inorganic pigment and/or powdered metal pigments.7. The water-absorbing resin according to claim 1 wherein saidhigh-molecular material contains 0.01 to 20 wt % of the inorganicpigment and/or powdered metal pigments.
 8. The water-absorbing resinaccording to claim 6 wherein said inorganic pigment and/or the powderedmetal pigments are at least one of carbon black, iron black, titaniumoxide, zinc flower, iron oxide red, ultramarine, berlin blue, cobaltblue, lithopone, zinc sulfide, antimony oxide, yellow iron oxide, amber,sienna, ochre, pyridian, aluminum powders or bronze powders.
 9. Thewater-absorbing resin according to claim 1 wherein introduction of saidionic group is by introducing an acidic group and/or hydrolysis.
 10. Thewater-absorbing resin according to claim 1 wherein said ionic group isat least one of a sulfonic acid group and/or its salt, a carboxylic acidand/or its salt, a —PO(OH)2 group and/or its group, a —CH2PO(OH)2 groupand/or its salt, a —NO2, a hydroxy group and its salt, or achlorometylated amine group and/or its salt.
 11. The water-absorbingresin according to claim 1 wherein said ionic group is introduced in anamount of 10 to 70 mol % based on the entire unit in the high-molecularmaterial.
 12. A method for manufacturing a water-absorbing resincomprising: processing a high-molecular material having acrylonitrile,styrene and a conjugated diene as constituent elements with an acidand/or alkali.
 13. The method for manufacturing a water-absorbing resinaccording to claim 12 wherein the processing with alkali and/or acid isby introducing an acidic group and/or by hydrolysis.
 14. The method formanufacturing a water-absorbing resin according to claim 12 wherein theprocessing with acid uses at least one inorganic acid selected from thegroup consisting of concentrated sulfuric acid, sulfuric anhydride,fuming sulfuric acid, chlorosulfonic acid, nitric acid, fuming nitricacid, phosphoric acid, phosphorus chloride and phosphorus oxide.
 15. Themethod for manufacturing a water-absorbing resin according to claim 12wherein the processing with acid uses 70 wt % concentrated sulfuricacid.
 16. The method for manufacturing a water-absorbing resin accordingto claim 12 wherein the processing with alkali and/or acid uses ahigh-molecular material sized to pass through mesh not less than 3.5.17. The method for manufacturing a water-absorbing resin according toclaim 12 wherein the conjugated diene part of the high-molecularmaterial constitutes a block copolymer.
 18. The method for manufacturinga water-absorbing resin according to claim 12 wherein saidhigh-molecular material contains 10 to 50 mol % of acrylonitrile, 30 to70 mol % of styrene and 5 to 50 mol % of conjugated diene.
 19. Themethod for manufacturing a water-absorbing resin according to claim 12wherein said high-molecular material is an acrylonitrile- butadiene-styrene resin.
 20. The method for manufacturing a water-absorbing resinaccording to claim 12 wherein said high-molecular material is a wastematerial comprised of a used resin molded for specified usage.
 21. Themethod for manufacturing a water-absorbing resin according to claim 12wherein said high-molecular material contains the inorganic pigmentand/or powdered metal pigments added thereto.
 22. The method formanufacturing a water-absorbing resin according to claim 12 wherein saidhigh-molecular material contains 0.01 to 20 wt % of the inorganicpigment and/or powdered metal pigments added thereto.
 23. The method formanufacturing a water-absorbing resin according to claim 21 wherein saidinorganic pigment and/or the powdered metal pigments are at least one ofcarbon black, iron black, titanium oxide, zinc flower, iron oxide red,ultramarine, berlin blue, cobalt blue, lithopone, zinc sulfide, antimonyoxide, yellow iron oxide, amber, sienna, ochre, pyridian, aluminumpowders or bronze powders.
 24. The method for manufacturing awater-absorbing resin according to claim 12 wherein said processing withacid and/or alkali introduces at least one substituent selected from thegroup consisting of a sulfonic acid group and/or its salt, a carboxylicacid or its salt, a —PO(OH)2 group and/or its group, a —CH2PO(OH)2 groupand/or its salt, a —NO2, a hydroxy group and its salt, or achloromethylated amine group and/or its salt.
 25. The method formanufacturing a water-absorbing resin according to claim 24 wherein saidsubstituent is introduced in an amount of 10 to 70 mol % to the entireunit in said high-molecular material.
 26. A water-absorbing resinwherein an ionic group is introduced into a high-molecular materialcontaining inorganic pigments and/or metal powders and acrylonitrile.27. The water-absorbing resin according to claim 26 wherein thehigh-molecular material contains 5 to 90 mol % o acrylonitrile.
 28. Thewater-absorbing resin according to claim 26 wherein the high-molecularmaterial contains at least one of styrene or conjugated diene.
 29. Thewater-absorbing resin according to claim 26 wherein the high-molecularmaterial contains not less than 20 to 95 mol % of at least one ofstyrene or conjugated diene.
 30. The water-absorbing resin according toclaim 26 wherein the high-molecular material is at least one of anacrylonitrile- butadiene- styrene resin, a styrene-acrylonitrile resinor acrylonitrile-butadiene rubber.
 31. The water-absorbing resinaccording to claim 26 wherein said high-molecular material contains 0.01to 20 wt % of the inorganic pigment and/or powdered metal pigments. 32.The water-absorbing resin according to claim 26 wherein said inorganicpigment and/or the powdered metal pigments are at least one of carbonblack, iron black, titanium oxide, zinc flower, iron oxide red,ultramarine, berlin blue, cobalt blue, lithopone, zinc sulfide, antimonyoxide, yellow iron oxide, amber, sienna, ochre, pyridian, aluminumpowders or bronze powders.
 33. The water-absorbing resin according toclaim 26 wherein the high-molecular material is a waste materialcomprised of a used resin molded for specified usage.
 34. Thewater-absorbing resin according to claim 26 wherein the ionic group isintroduced in an amount of 5 to 95 mol %.
 35. The water-absorbing resinaccording to claim 26 wherein the ionic group is at least one of asulfonic acid group, a —PO(OH)2 group, a —CH2(PO(OH)2 group, a —NO2, ahydroxy group, or a chloromethylated amine group.
 36. A method formanufacturing a water-absorbing resin comprising: processing ahigh-molecular material containing an inorganic pigment and/or metalpowder pigments and acrylonitrile with an alkali and/or an acid tointroduce an ionic group.
 37. The method for manufacturing awater-absorbing resin according to claim 36 wherein said processing withacid is by at least one organic acid.
 38. The method for manufacturing awater-absorbing resin according to claim 37 wherein said inorganic acidis at least one of concentrated sulfuric acid, sulfuric anhydride,fuming sulfuric acid, chlorosulfonic acid, nitric acid, fuming nitricacid, phosphoric acid, phosphorus chloride and phosphorus oxide.
 39. Themethod for manufacturing a water-absorbing resin according to claim 36wherein said high-molecular material is dispersed in a sulfonating agentto introduce a sulfonic acid group.
 40. The method for manufacturing awater-absorbing resin according to claim 36 wherein, in said processingwith acid, one of concentrated sulfuric acid or chlorosulfonic acid isfirst added and subsequently one of sulfuric anhydride or fumingsulfuric acid is added.
 41. The method for manufacturing awater-absorbing resin according to claim 36 wherein said high-molecularmaterial is dispersed in a solvent to introduce ionic groups.
 42. Themethod for manufacturing a water-absorbing resin according to claim 37wherein the processing with alkali and/or acid uses a high-molecularmaterial sized to pass through mesh not less than 3.5.
 43. The methodfor manufacturing a water-absorbing resin according to claim 36 whereinsaid high-molecular material contains 5 to 80 mol % of acrylonitrile.44. The method for manufacturing a water-absorbing resin according toclaim 36 wherein said high-molecular material contains at least one ofstyrene or conjugated diene.
 45. The method for manufacturing awater-absorbing resin according to claim 36 wherein material saidhigh-molecular material contains 20 to 95 mol % of at least one ofstyrene or conjugated diene.
 46. The method for manufacturing awater-absorbing resin according to claim 36 wherein said high-molecularmaterial is at least one of an acrylonitrile- butadiene- styrene resin,a styrene- acrylonitrile resin or acrylonitrile-butadiene rubber. 47.The method for manufacturing a water-absorbing resin according to claim36 wherein said high-molecular material contains 0.01 to 20 wt % of theinorganic pigment and/or powdered metal pigments.
 48. The method formanufacturing a water-absorbing resin according to claim 36 wherein saidinorganic pigment and/or the powdered metal pigments are at least one ofcarbon black, iron black, titanium oxide, zinc flower, iron oxide red,ultramarine, berlin blue, cobalt blue, lithopone, zinc sulfide, antimonyoxide, yellow iron oxide, amber, sienna, ochre, pyridian, aluminumpowders or bronze powders.
 49. The method for manufacturing awater-absorbing resin according to claim 36 wherein the high-molecularmaterial is a waste material comprised of a used resin molded forspecified usage.
 50. The method for manufacturing a water-absorbingresin according to claim 36 wherein the ionic group is introduced in anamount of 5 to 95 mol %.
 51. The method for manufacturing awater-absorbing resin according to claim 36 wherein the ionic group isat least one of a sulfonic acid group, a carboxylic acid group, a—PO(OH)2 group, a —CH2(PO(OH)2 group, a —NO2, a hydroxy group, or achloromethylated amine group.
 52. A water-absorbing resin mainlycontaining a high-molecular material having an ionic group introducedtherein and also containing a stabilizer.
 53. The water-absorbing resinaccording to claim 52 wherein the content of said stabilizer on the dryweight basis is 0.00001 to 20 wt %.
 54. The water-absorbing resinaccording to claim 52 wherein said stabilizer is at least one of aphenolic antooxidant, a sulfur-based anti-oxidant or a phosphorus-basedanti-oxidant.
 55. The water-absorbing resin according to claim 52wherein said stabilizer is at least one selected from the groupconsisting of erysorbic acid, sodium erysorbate and isopropyl citrate.56. The water-absorbing resin according to claim 52 wherein saidstabilizer is at least one selected from the group consisting of abenzophenone based light stabilizer, a benzotriazole based lightstabilizer, a hindered amine based light stabilizer, a cyano-acrylatebased light stabilizer, salicylate based light stabilizer or an oxalicacid anilide based light stabilizer.
 57. The water-absorbing resinaccording to claim 52 wherein the ionic group is at least one of asulfonic acid group, a chloromethylated amine group, a carboxylic group,a hydroxy group, a —PO(OH)2 group, a —CH2PO(OH)2 group or a —NO2. 58.The water-absorbing resin according to claim 52 containingacross-linkedpolymer of polyacrylic acid and/or its salt as ahigh-molecular material in which is introduced said ionic group.
 59. Thewater-absorbing resin according to claim 52 containing a polymer,obtained on graft polymerization of acrylic acid and/or its salt tostarch and/or polyvinyl alcohol, as the high-molecular material in whichis introduced said ionic group.
 60. The water-absorbing resin accordingto claim 52 containing a cross-linked polymer of polyvinyl alcohol as ahigh-molecular material in which is introduced said ionic group.
 61. Thewater-absorbing resin according to claim 52 containing a hydrolyzate ofa polymer containing acrylonitrile as a constituent unit as thehigh-molecular material in which is introduced said ionic group.
 62. Thewater-absorbing resin according to claim 61 wherein the polymercontaining acrylonitrile as the constituent unit contains acrylonitrilein an amount of 2 to 95 mol %.
 63. The water-absorbing resin accordingto claim 61 wherein the polymer containing acrylonitrile as theconstituent unit also contains at least one of styrene or conjugateddiene in addition to acrylonitrile.
 64. The water-absorbing resinaccording to claim 61 wherein the polymer containing acrylonitrile asthe constituent unit is at least one selected from the group consistingof polyacrylonitrile, an acrylonitrile- butadiene- styrene resin, astyrene- acrylonitrile resin or acrylonitrile-butadiene rubber.
 65. Amethod for manufacturing a water-absorbing resin comprising: introducinga stabilizer into a high-molecular material into which is previouslyintroduced an ionic group.
 66. A method for manufacturing awater-absorbing resin comprising: hydrolyzing a stabilizer-containinghigh-molecular material to introduce an ionic group.
 67. The method formanufacturing a water-absorbing resin according to claim 66 wherein saidhigh-molecular material is a polymer containing acrylonitrile as aconstituent unit.
 68. The method for manufacturing a water-absorbingresin according to claim 66 wherein said hydrolysis is carried out usingat least one of concentrated sulfuric acid, sulfuric anhydride, fumingsulfuric acid, chlorosulfonic acid, nitric acid, fuming nitric acid,phosphoric acid, phosphorus chloride or phosphorus oxide
 69. The methodfor manufacturing a water-absorbing resin according to claim 66 whereinsaid stabilizer-containing high-molecular material is a waste materialcomprised of a used resin.